The field of the disclosure relates generally to interior lighting systems, and, more particularly, to systems for providing interior lighting in the passenger cabin of an aircraft.
Aircraft passenger cabins are known to have lighting fixtures designed to illuminate a specific targeted area, such as for reading, sometimes referred to as “task” lighting. Aircraft passenger cabins also are known to have lighting fixtures that direct light along the surfaces of walls and ceilings, sometimes referred to as “general” or “wash” lighting. The illumination pattern produced by the wash lighting is considered to have an effect on the mood and wellbeing of the passengers.
Traditionally, fluorescent lamps have been used for providing wash lighting, such as along the ceiling of an aircraft passenger cabin. A typical aircraft cabin arrangement is to have one or two rows of fluorescent tubes extending along the edge of the ceiling panels for each aisle along the length of the passenger cabin, parallel to the aircraft centerline. The fluorescent tubes themselves are generally hidden from direct view by shielding them behind a valance or similar device. However, a significant proportion of the generated light is thus blocked without providing any useful interior lighting. Moreover, fluorescent lamps generate a high light intensity on surfaces near the lamp, and a dramatically lower intensity (which decreases in proportion to the square of the distance from the lamp surface) on surfaces farther away from the lamp. This wide variation in surface brightness may not be ideal for the comfort of the passengers.
It is also known to use light emitting diode (LED) fixtures as a supplement or replacement for fluorescent lamps to provide wash lighting. For example, it is known to use a combination of LEDs producing light of different wavelengths in order to provide wash lighting with a desired color balance. It is also known to supplement fluorescent lighting with LEDs outputting light through a light guide element with a U-shaped cross section, with the parallel ends of the “U” serving as the light exit surfaces. While these arrangements permit a variation of light output intensity from the LED output point over time, however, they still provide no means to control the varying intensity distribution along the wash-lighted surface at any given time due to the decrease in intensity with distance from the output point.
At least some known wash lighting systems provide for wash lighting using a lens assembly to focus more light intensity to a particular area. However, such known lens systems are not tuned to provide a desired surface intensity profile across a particular surface. In addition, at least some known wash lighting systems route the output of an LED through a micro lens assembly in a compact lighting fixture. Rather than extending parallel to the aircraft centerline like a traditional fluorescent lamp, the compact lighting fixture produces a desired illumination pattern on a smaller surface area. For example, multiple compact lighting fixtures positioned a certain distance apart from each other relative to an axis parallel to the aircraft centerline are needed to provide illumination along the full extent of the passenger cabin ceiling. The multiple compact lighting fixtures create slightly overlapping patterns that inhibit providing a uniform light distribution along the extent of the surface. Moreover, the compact lighting fixtures do not fit the traditional geometry of wash lighting fixtures. Thus, in some circumstances it may be desirable to provide a wash lighting device that extends longitudinally, similarly to a traditional fluorescent lamp, and provides for a uniform intensity distribution, or other desired intensity distribution, of wash lighting.